Sensor And Sensing System For Respirator Fit-Test Method

ABSTRACT

There is provided a sensor including a housing, where the housing has an opening configured to receive a sensing element; an electric circuit operably connected to the housing, where the electric circuit is configured to detect at least one electrical characteristic across at least one pair of electrodes positioned on the sensing element; at least one gas-moving element in electrical communication with the electric circuit; and a reader in communication with the electric circuit, where the reader is configured to compare information about a gas volume external to the housing with information about a gas volume within the housing.

BACKGROUND

Particulate matter (PM) sensors are sensing elements that are configuredto enable quantification of the concentration of particles in anenvironment, most commonly an environment where particles are suspendedin a gas phase. PM sensors have received an increase in attention overthe last decade as a result of increased awareness of the possibleimpact of PM on human health. PM sensors are commonly used to enableenvironmental PM monitoring, diesel engine soot particle output,particle filter efficiency measurements, and respirator fit testing.Most of the sensor systems fall into one of the following categories: 1)mass based measurements, which monitor the mass of particles depositedover time by use of a mass balance or quartz crystal microbalance(typically used in environmental monitoring), 2) optical basedmeasurements, where an optical signal is used to monitor theconcentration of particles in an airstream (typically used inenvironmental monitoring and quantitative respirator fit testing), and3) electrical conductivity sensing, where the deposition of electricallyconductive particles on a pair of electrodes results in a measurableelectrical signal (typically used in diesel engine soot monitoring,because soot particles are electrically conductive).

SUMMARY

The present disclosure relates to fit-test methods for a respirator. Inparticular, this disclosure relates to an aerosol generator with a knownaerosol output parameter; an enclosure that is physically supportedaround the wearer's head, where the aerosol generator provides the knownaerosol output parameter at least partially contained within theenclosure around wearer's head; a sensor comprising a sensing elementoperably connected to the respirator, where the sensor is configured tomonitor a particulate concentration parameter within the respirator; anda reader configured to communicate with the sensor, where the reader isconfigured to provide a respirator fit parameter based on a comparisonof the particulate concentration parameter to the known aerosol outputparameter.

In one aspect, the present disclosure provides a sensor comprising: ahousing, wherein the housing has an opening configured to receive asensing element; an electric circuit operably connected to the housing,wherein the electric circuit is configured to detect at least oneelectrical characteristic across at least one pair of electrodespositioned on the sensing element; at least one gas-moving element inelectrical communication with the electric circuit; and a reader incommunication with the electric circuit, wherein the reader isconfigured to compare information about a gas volume external to thehousing with information about a gas volume within the housing. In someembodiments, the opening is substantially rectangular in shape. In someembodiments, the sensing element is substantially rectangular in shape.

In some embodiments, a detection surface of the sensing elementcomprises the at least one pair of electrodes. In some embodiments, thehousing further comprises at least one gas intake opening and at leastone gas exhaust opening configured to direct a predetermined flow rateof gas to contact the detection surface of the sensing element afterwhich the predetermined flow rate of gas is forced out of the housing bythe gas-moving element. In some embodiments, the detection surface ofthe sensing element is oriented substantially perpendicular to thepredetermined flow of gas.

In some embodiments, the electric circuit is affixed to the housing. Insome embodiments, the electric circuit is positioned within the housing.In some embodiments, the electric circuit is affixed to at least oneinterior wall of the housing. In some embodiments, when the sensingelement is inserted in the opening, there is substantially no fluidcommunication from the outside of the housing to the inside of thehousing through the interstitial space between the opening and thesensing element.

In some embodiments, the gas comprises particulates. In someembodiments, the electrical characteristic is at least one ofresistance, inductance, capacitance, and electrical impedance. In someembodiments, the sensor comprises a heating element configured toincrease the temperature of at least a portion of a sensing elementsurface. In some embodiments, the sensor is configured to applyelectrical power to at least one heating element on the sensing element.In some embodiments, a respirator fit test system comprises any of theaforementioned sensor embodiments.

The above summary is not intended to describe each embodiment or everyimplementation of the present disclosure. A more complete understandingwill become apparent and appreciated by referring to the followingdetailed description and claims taken in conjunction with theaccompanying drawings. In other words, these and various other featuresand advantages will be apparent from a reading of the following detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of top, front and side view of anillustrative sensing element.

FIG. 2 are schematic diagrams of top views of two illustrative sensingelements.

FIG. 3 is a schematic diagram cross-sectional view of an illustrativesensing element.

FIG. 4A is a schematic diagram of top, front and side view of anotherillustrative sensing element.

FIG. 4B is a schematic diagram of top, front and side view of anotherillustrative sensing element.

FIG. 5A is a flow diagram of an illustrative method of making a sensingelement.

FIG. 5B is a flow diagram of another illustrative method of making asensing element.

FIG. 6 is a schematic diagram cross-sectional view of the sensingelement of FIG. 4A illustrating fluid disposed on the electrode pairstructures.

FIG. 7 is a schematic diagram cross-sectional view of an illustrativesensing element with a filtering element.

FIG. 8 is a schematic diagram cross-sectional view of the sensingelement of FIG. 7 illustrating fluid disposed on the electrode pairstructures.

FIG. 9 is a schematic diagram of top view of another illustrativesensing element.

FIG. 10 is a schematic diagram of top view of another illustrativesensing element.

FIG. 11 are graphs illustrating the sensor response to differentconcentrations of NaCl in water, the top three graphs illustrate theresistance (solid lines) and reactance (dashed lines), as a function offrequency, measured by the sensor when coated with a liquid layer of thesolution indicated. The bottom three graphs illustrate the impedancemagnitude (solid lines) and phase shift (dashed lines), as a function offrequency, measured by the sensor when coated with a liquid layer of thesolution indicated. Z=impedance magnitude, Theta=phase shift,R=resistance, and X=reactance.

FIG. 12A-12C are graphs that illustrate a comparison of isothermal wateruptake and NaCl aerosol response for different surface modification andcoating systems applied to a salt aerosol sensor.

FIG. 13A-13D are graphs that illustrate a comparison of isothermal wateruptake and NaCl aerosol response for a zwitterionic siloxane surfacefollowed by different coat weights of glucose applied to a salt aerosolsensor.

FIG. 14A-14C are graphs that illustrate a comparison of isothermal wateruptake and NaCl aerosol response for sensors with and without a filterelement.

FIG. 15 is a schematic diagram of an illustrative respirator sensorsystem.

FIG. 16A is schematic diagram of an illustrative respirator sensorsystem corresponding to a method useful in the present disclosure.

FIG. 16B is schematic diagram of an illustrative respirator sensorsystem corresponding to a method useful in the present disclosure.

FIG. 17 is schematic diagram of an illustrative respirator sensor systemcorresponding to a method useful in the present disclosure.

FIG. 18 is a schematic diagram of an illustrative sensor.

FIG. 19 is a schematic diagram of an illustrative sensor including anillustrative sensing element.

FIG. 20 is a schematic diagram of an illustrative sensing element withan added spacer layer, filtering element, and electrical bridge.

FIG. 21 is a schematic diagram of an illustrative sensor system using asensing element with some of the described components.

FIG. 22 is a schematic diagram of an illustrative sensor system with agas transport structure.

FIG. 23 is a schematic diagram of an illustrative internal structure ofa gas transport structure.

FIG. 24 is a schematic diagram of an illustrative sensor with a batteryand charging port.

FIG. 25 is a schematic diagram of an illustrative housing for a sensor.

FIG. 26 is a schematic diagram of an illustrative sensor including asensing element with an extended tab.

FIG. 27 is a schematic diagram of an illustrative sensor showinginsertion and removal of a sensing element.

FIG. 28 is a schematic diagram of an illustrative sensor including ahousing with an annular fluid channel.

FIG. 29 is a schematic diagram of an illustrative sensor including ahousing with separable elements.

FIG. 30 is a schematic diagram of an illustrative sensor including atransport control structure.

FIGS. 31A-D show data comparing sodium chloride aerosol detection of thepresently disclosed sensor to a sodium flame photometer when the sensoris mounted in the interior space of a respirator.

FIG. 32 is a schematic illustrative sensor including at least oneheating element.

FIGS. 33A-D show data comparing sodium chloride aerosol detection of thepresently disclosed sensor to a sodium flame photometer when the sensoris mounted on the exterior of a respirator.

FIG. 34 show data for sensor signals when a wearer conducts exercisessuch as those prescribed by US Occupational Safety and HealthAdministration in 30 CFR 1910.134 Appendix A.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof, and in which are shown byway of illustration several specific embodiments. It is to be understoodthat other embodiments are contemplated and may be made withoutdeparting from the scope or spirit of the present disclosure. Thefollowing detailed description, therefore, is not to be taken in alimiting sense.

All scientific and technical terms used herein have meanings commonlyused in the art unless otherwise specified. The definitions providedherein are to facilitate understanding of certain terms used frequentlyherein and are not meant to limit the scope of the present disclosure.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the properties sought tobe obtained by those skilled in the art utilizing the teachingsdisclosed herein.

The recitation of numerical ranges by endpoints includes all numberssubsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3,3.80, 4, and 5) and any range within that range.

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” encompass embodiments having pluralreferents, unless the content clearly dictates otherwise.

As used in this specification and the appended claims, the term “or” isgenerally employed in its sense including “and/or” unless the contentclearly dictates otherwise.

As used herein, “have”, “having”, “include”, “including”, “comprise”,“comprising” or the like are used in their open-ended sense, andgenerally mean “including, but not limited to”. It will be understoodthat “consisting essentially of”, “consisting of”, and the like aresubsumed in “comprising,” and the like.

A fluid-soluble particle is any particle that may dissolve in the fluid.A fluid-ionizable particle is one that, it addition to dissolving, alsoionizing to some extent. Particles may dissolve, but not ionize (such asour hygroscopic layer). In some instances, in the present disclosure,the terms “fluid-soluble” and “fluid-ionizable” are usedinterchangeably.

As used herein, the term “gas” includes materials that are gaseous atambient conditions and aerosols. However, in some embodiments, the term“gas” does not include materials that are liquid at ambient conditions.The term “aerosol” as used herein means a two-phase system at ambientconditions, where one phase is a continuous phase, such as a gas (i.e.,air or a propellant gas) the other phase is a dispersed phase, such assolid particles, liquid particles, liquid particles that change to solidparticles in situ, solid particles that change to liquid particles insitu, or any combinations thereof.

The present disclosure relates to fit-test methods for a respirator. Inparticular, this disclosure relates to a fit-test method utilizing anelectronic sensing system configured to wirelessly communicate with areader and detect a change in an electrical property (resistance,capacitance, inductance or other AC impedance properties) of a sensorpositioned substantially within an interior gas space of the respiratoror mounted substantially on an exterior surface of the respirator. Amethod of fit-testing includes providing a respirator; providing asensor having a sensing element removably positioned substantiallywithin an interior gas space of the respirator or mounted substantiallyon an exterior surface of the respirator; providing a reader configuredto be in communication with the sensor; positioning the respirator overa mouth and a nose of a user while the sensor is positionedsubstantially within an interior gas space of the respirator or mountedsubstantially on an exterior surface of the respirator; and observingrespirator fit assessment data communicated from the sensor to thereader. Another method of fit-testing includes providing a respirator;providing a sensor comprising a sensing element removably positionedsubstantially within an interior gas space of the respirator or mountedsubstantially on an exterior surface of the respirator; providing areader configured to be in communication with the sensor; positioningthe respirator over a mouth and a nose of a user while the sensor ispositioned substantially within an interior gas space of the respiratoror mounted substantially on an exterior surface of the respirator; andobserving respirator fit assessment data communicated by the reader; andcapturing an image of the correct fit position on the user's face oncethe sensor indicates a pre-determined fit assessment data value has beenreached. In some embodiments, the sensing element is mounted within theinterior gas space of the respirator and the sensor is mounted on theexterior surface, such that the sensor can wirelessly monitor a signalfrom the sensing element using inductance, near field coupling, and thelike.

In some embodiments, a method for detecting fluid ionizable particles ina gaseous medium includes, contacting a gaseous medium with a fluidionizable particulate matter sensing element; condensing a component ofthe gaseous medium on at least a portion of the fluid ionizableparticulate matter sensing element; determining an electrical propertybetween a first pair of electrodes of the fluid ionizable particulatematter detection element; determining an electrical property between asecond pair of electrodes of the fluid ionizable particulate matterdetection element; and determining a value related to the presence offluid ionizable particles in the gaseous medium at least partially bycomparing the value of the electrical property of the first pair ofelectrodes to the electrical property of the second pair of electrodes.In some embodiments, the reader is configured to be in wirelesscommunication with the sensor. In some embodiments, the reader is on thesame electric circuit as the sensor. A system for fit-testing arespirator includes, a respirator, a sensor including a sensing element,and a reader configured to be in communication with the sensor. Thesensor is positioned substantially within an interior gas space of therespirator or mounted substantially on an exterior surface of therespirator. In some embodiments, the system also includes an enclosuremountable on the head and/or shoulders of a wearer. In some embodiments,the system further includes an aerosol generator used to deliver aerosolwith a known aerosol output parameter that is at least partiallycontained within the enclosure around wearer's head. The sensing elementmay be configured to enable compensation of background noise induced byenvironmental factors, for example, temperature, humidity, and gaseouscomponent interactions. The electronic sensing element may also beconfigured to be easily plugged into and removed from a sensor to enablereadout of the sensing element signal. In some cases, the sensor maycommunicate with other components in the system via wirelesscommunication, enabling a completely wireless aerosol monitoring system,with disposable sensor elements, that may be configured to be integratedwith a respiratory protection device. The electronic sensing element mayenable the electrical detection of some particles which arenon-conducting in the solid particle state, and also provides a means ofbackground compensation for environmental changes. The electronicsensing element is configured to detect particles which dissolve intoconductive components in a fluid. For example, crystalline saltparticles, such as sodium chloride particles, are electricallyinsulating in the solid particle state, but dissolve into conductivesodium and chloride ions in polar fluids, such as water. The sensingelement enables detection of these particles because the surface of thesensing element is designed such that a fluid film forms in the regionbetween the electrodes. When the particles of interest impact thesensing element, they dissolve into the fluid, which then enablesdetection. The sensing element may be designed such that the fluid filmforms from gases in the environment. As an example, the fluid may beformed by the condensation of water vapor from human breath. In thisexample, the sensing may be placed inside or mounted substantially onthe exterior of a respirator for use in respirator fit-testing.Aerosolized salt particles which leak into the respirator may impact thesensing element surface, which has a fluid layer formed by the watervapor in the exhaled breath of the wearer, to enable leak detection ofthe respirator.

Background compensation may be provided by a second pair of electrodeson the sensing element surface (although the two pairs of electrodes mayshare a single common ground element). This second pair of electrodes,the reference electrodes, may have a particle filtering element abovethe surface of the electrode pair which may prevent the particles ofinterest from interacting with the reference electrodes. However, withappropriate pressure drop of the filtering element, the same gaseouscomponents which interact with the first pair of electrodes may be ableto pass through the filter and also interact with the second pair ofreference electrodes. The surface modification surrounding the electrodepairs may be patterned such that there is a discontinuity in the fluidbetween the electrode pairs. This discontinuity may prevent themigration of elements from one electrode pair to the other. Thisassembly results in a reference electrode pair which experiences theenvironmental effects experienced by the first electrode pair, but alesser amount of the particulate effects. This enables a way of removingthe environmental effects from the signal recorded by the first pair ofelectrodes. In some embodiments, the reference electrode pair may havethe particulate material of interest predisposed on the surface, suchthat the background compensation signal includes the environmentalinteraction with the PM of interest. For example, if the sensing elementis configured to monitor sodium chloride particles, the reference pairmay be pre-loaded with a known amount of sodium chloride, so that whenthe signal from the first pair of electrodes matches the signal from thereference pair, it can be inferred that the first pair of electrodes hasthe same quantity of sodium chloride as the reference pair. While thepresent disclosure is not so limited, an appreciation of various aspectsof the disclosure will be gained through a discussion of the examplesprovided below.

FIG. 1 is a schematic diagram of top, front and side view of anillustrative sensing element 10. The sensing element 10 is configured tointeract with an environment of interest. The sensing element 10includes a substrate 1 having an electrically non-conductive surface 11,at least one high surface energy region 3, and an electrode pairstructure 2 disposed on the electrically non-conductive surface 11. Theelectrode pair structure 2 includes at least one pair of electrodes A, Bhaving a gap 12 therebetween. At least one of the electrodes A or B isat least partially within the at least one high surface energy region 3.The sensing element 10 is configured to sense fluid-soluble particulatematter.

At least some of the high surface energy region 3 may be overlapping andadjacent to the electrode pair structure 2 or the electrode pair A, B,and may be configured to interact with an environment of interest, by,for example, promoting the condensation of gaseous molecules orparticulate matter into a condensed fluid on the high surface energyregion 3 and particularly within the gap 12 of the electrode pairstructure 2 or the electrode pair A, B, or promoting the sensitivity toa component of interest.

Fluid-ionizable particulate matter is particulate matter that may, ormay not, be electrically conductive in the solid-state form, but mayionize into electrically conductive components in a fluid, such aswater. Dissolution of the fluid-soluble particulate matter in the fluidmay provide a change in an electrical property of the liquid that may bedetected or sensed by the electrode pair structure 2. One usefulfluid-soluble particulate matter is sodium chloride (NaCl).

The electrodes A and B in the at least one pair of electrodes A, B maybe co-planar with respect to each other. The electrodes A and B in theat least one pair of electrodes A, B may be parallel extending orinterdigitated, or have any other useful configuration. The gap 12defined by a distance between the electrodes A and B in the at least onepair of electrodes A, B may have a lateral distance G_(L) value of anyuseful value. This lateral distance G_(L) value may be in a range from25 to 125 micrometers. The electrodes may have any useful lateral widthE_(L) value. This lateral width E_(L) value may be in a range from 25 to125 micrometers. The electrodes A and B may be formed of anyelectrically conducting and corrosion or oxidation resistant materialsuch as various metals or metal alloys.

The high surface energy region 3 may be patterned onto the substrate 1or electrically non-conductive surface 11 to provide for selectivedeposition of liquid onto the substrate 1 or electrically non-conductivesurface 11 for contacting the electrode pair structure 2. The highsurface energy region 3 may be at least partially, or completelysurrounded or circumscribed by one or more low surface energy regions 6.The high surface energy region 3 may provide for selective deposition ofliquid or water to form a liquid layer or liquid volume within the gap12 of the electrode pair structure 2 onto the high surface energy region3. Thus, the liquid layer or liquid volume may contact both electrodes Aand B in the electrode pair structure 2. The high surface energy region3 may define any useful shape or surface area.

The phrase “high surface energy region” refers to a surface region thatexhibits an advancing water contact angle of less than 90 degrees, orless than 80 degrees, or less than 60 degrees, and/or preferably lessthan 45 degrees, as measured per ASTM D7334. It is noted that a watervolume of 20 microliters, which is a general recommendation in ASTMD7334-08, may be too large for proper testing depending on the surfacegeometry. It is necessary that the water volume is small enough inrelation to the size of the surface region such that the advancingcontact angle is not disturbed by the confinement of the region.

The phrase “low surface energy region” refers to a region with lowersurface energy than the high surface energy region, such that the lowsurface energy region has an advancing water contact angle that isgreater than that of the high surface energy region. The low surfaceenergy region may have an advancing water contact angle that is 1-10degrees, or 10-20 degrees, or 20-45 degrees, and/or preferably more than45 degrees, greater than that of the high surface energy region.

For example, the high surface energy region 3 may have an advancingwater contact angle of 20 degrees, and the low surface energy region 6may have an advancing water contact angle of 60 degrees. In anotherexample, the high surface energy region 3 may have an advancing watercontact angle of 70 degrees, and the low surface energy region 6 mayhave an advancing water contact angle of 100 degrees. The difference inadvancing water contact angles promotes confinement of a condensed fluidto the predefined regions, which may minimize undesirable interactions.The advancing water contact angle may be impacted by the hydrophilicnature of the surface region, or the hygroscopic nature of materials inthe surface region which effectively alter the advancing water contactangle.

The high surface energy region 3 may be formed by surface treatment ofthe substrate 1 or electrically non-conductive surface 11. These surfacetreatments include, for example, plasma, chemical modification, and thelike. Plasma treatments may include oxygen plasma treatment. Chemicaltreatment includes deposition or vapor deposition of silanes orsiloxanes to form, for example, a siloxane surface or a zwitterionicsiloxane surface defining the high surface energy region 3. Chemicaltreatment may also, or alternatively, include deposition of hygroscopicmaterials to define the high surface energy region 3. The high surfaceenergy region 3 may have a dissolvable ion content of less than 1E-9moles/mm². For example, a 1 mm² surface region with 10 ng of sodiumchloride has a dissolvable ion content of approximately 3.45E-10moles/mm² (1.72E-10 moles/mm² contributed by sodium and 1.72E-10moles/mm² contributed by chloride) due to the potential dissociation ofthe sodium chloride into sodium and chloride ions when water condenseson the region. The dissolvable ion content impacts the surfaceresistivity of the sensor. However, the surface resistivity is alsoimpacted by the ambient environment, such as the relative humidity, dueto the varied interactions of the high surface energy region 3 with theenvironment. For example, for the case of a 1 mm² surface region with 10ng of sodium chloride, the surface resistivity will be large in lowhumidity environments in which the sodium chloride remains a crystallinesolid, and the surface resistivity will be lower in high humidityenvironments in which the sodium chloride absorbs moisture from the airand dissolves into a liquid solution. The dissolvable ion content isalso impacted by the ionic dissociation constant of the species in thehigh surface energy region. For example, sodium chloride has a largeionic dissociation constant in water, while the ionic dissociationconstant of a compound such as glucose is much lower. As a result, foran equivalent molar amount of glucose loaded on a surface, thedissolvable ion content of the glucose surface will be significantlylower than that of a surface with sodium chloride.

Hygroscopic materials include materials which absorb or adsorb waterfrom the surrounding environment, and preferably those which absorb oradsorb water vapor from the surrounding gaseous medium. For example, thehygroscopic material may be a salt, an acid, a base, or preferably acompound with a low ionic dissociation constant in water such as awater-absorbing polymer, a monosaccharide, a polysaccharide, an alcohol,or more preferably a polyol, such that the surface resistivity change ofthe sensor due to absorption or adsorption of water is minimized.

The polyol may be a polymeric polyol or a monomeric polyol and maypreferably be a sugar alcohol, such as sorbitol. The hygroscopic layeris preferably a compound which enhances water retention and may also bewithin the class of compounds known as humectants. The hygroscopicmaterial is preferably a material which has a deliquescence point ofless than 100 percent relative humidity, or less than 90 percentrelative humidity, or more preferably less than 80 percent relativehumidity at 25 degrees Celsius and 1 atmosphere of pressure. Thedeliquescence point is taken to refer to the relative humidity at whichthe material absorbs enough water from the surrounding gaseous mediumsuch that it dissolves and forms a liquid solution. The formation of theliquid solution may enhance the performance of the fluid ionizableparticulate matter sensing element by providing a liquid solution that aparticle may dissolve into. The hygroscopic material and coating weightare preferably chosen such that the electronic mobility of the ions ofthe dissolved particulate matter of interest is minimally decreased bythe effects of the hygroscopic material.

The substrate 1 may be formed of any electrically non-conductivematerial. The substrate 1 may be a laminate or a single materialconstruction. The substrate 1 may be formed of any material used ascircuit board or electrical sensor substrates. The substrate 1 may beformed of any glass or dielectric resin. Illustrative substrate 1material is commercially available from Advanced Circuits, Colorado,USA, among other printed circuit board fabrication entities.

FIG. 2 are schematic diagrams of top views of illustrative sensingelements 10. The sensing element 10 includes a substrate 1 comprising anelectrically non-conductive surface 11, at least one high surface energyregion 3, and an electrode pair structure 2 disposed on the electricallynon-conductive surface 11, as described above. The electrode pairstructure 2 includes at least one pair of electrodes A, B having a gap12 therebetween. At least one of the electrodes A or B is at leastpartially within the at least one high surface energy region 3, asdescribed above. The sensing element 10 is configured to sensefluid-soluble particulate matter.

FIG. 2 on the left illustrates an interdigitated electrode pair A, Bhaving two opposing pairs of interdigitated members A2 and B2. The gap12 between interdigitated members A2 and B2 may have a lateral distancevalue of any useful value. This distance value may be in a range from 25to 125 micrometers. The interdigitated members A₂ and B₂ may have anyuseful lateral width. This lateral width may be in a range from 25 to125 micrometers. The interdigitated members A₂ and B₂ may have anyuseful length such as a range from 500 to 10,000 micrometers. Theinterdigitated members A₂ and B₂ may be formed of any electricallyconducting and corrosion or oxidation resistant material such as variousmetals or metal alloys. The interdigitated electrode pair A, B is shownwith four interdigitated members however the interdigitated electrodepair A, B may have any number of total interdigitated members, such asin a range from 2 to 50, or 4 to 40.

FIG. 2 on the right illustrates another embodiment of the sensingelement 10 where the electrode pair structure 2 defines a firstelectrode B at least partially surrounding a second electrode A anddefining a gap 12 therebetween.

FIG. 3 is a schematic diagram cross-sectional view of one illustrativesensing element 10. FIG. 3 provides an illustration of a suitablelayering structure that can be applied to the electricallynon-conductive surface 11 and electrode pair structure 2 to define thehigh surface energy region 3 and enhance the electrical impedanceresponse to a fluid soluble target particulate material such as a saltaerosol, for example. The electrode pair structure 2 includes at leastone pair of electrodes A, B having a gap 12 therebetween.

An illustrative surface treatment layer 120 may include a zwitterionicsilane layer or surface chemically grafted to a siloxane layer orsurface (where the siloxane surface may be formed by anoxygen+tetramethyl silane plasma treatment as illustrated in FIG. 5A).This illustrative surface treatment layer 120 may be referred to as asilane surface treatment layer 120. This illustrative surface treatmentlayer 120 may exist predominantly on the surface of the electricallynon-conductive surface 11 in between electrode pair structure 2 orbetween at least one pair of electrodes A, B or within the gap 12. Theillustrative surface treatment layer 120 may define the high surfaceenergy region 3.

FIG. 5A is a flow diagram of a process for forming the illustrativesurface treatment layer 120. This process includes forming electrodes A,B on the electrically non-conductive surface 11 at step 210. Then amasking layer is applied to define the high surface energy region on theelectrically non-conductive surface 11 at step 220, such that at leastone electrode A or B is at least partially within the defined highsurface energy region. The masking layer may be applied to theelectrically non-conductive surface 11, such that some region of theelectrically non-conductive surface 11 is exposed to the subsequenttreatments, and some regions are protected from the subsequenttreatments. The regions protected from subsequent treatments may formlow surface energy regions. A suitable masking layer is any layer thatforms a desired pattern for forming the desired surface composition andmay resist plasma treatment in defined locations. For example, asuitable masking layer is a tape commercially available under the tradedesignation “3M Vinyl Tape 491” from 3M, MN, USA.

The masked article is placed in a vacuum chamber at step 230. The vacuumchamber may provide a vacuum environment of 100 mTorr or less, or 50mTorr or less. Then an oxygen plasma is applied to the masked article atstep 231. Oxygen gas (for example, at a concentration of 500 parts permillion (ppm)) may be introduced and formed into a plasma in fluidcontact with at least some of the electrode surface for a period of time(for example, sixty seconds). In certain embodiments, the plasma may begenerated by applying a 500 W radiofrequency field. Then a silane isdeposited or vapor deposited onto the plasma treated article at step232. Tetramethyl silane (for example, at a concentration of 150 ppm) maybe added to the plasma for a period of time (for example, thirtyseconds). The tetramethylsilane flow may be interrupted, and oxygenplasma continues for a period of time (for example, sixty seconds). Thesecond oxygen plasma is applied to the masked article at step 233. Thenthe plasma treated article is removed from the vacuum chamber at step234.

Then a zwitterionic silane solution is coated onto the treated articleat step 240. The solution containing a zwitterionic silane, for exampleat 2 wt % in water, is applied in fluid contact with the sensing elementsurface for a period of time (for example, ten seconds). The coatedarticle is blown dry at step 241 and then baked at an elevatedtemperature for a period of time (for example, ten minutes at 110° C.).The sensing element 10 is then rinsed at step 250 with deionized waterand dried at step 251.

The silane surface treatment layer 120 may be formed of compounds havingformula (I) as described in International Patent Publication No.WO2016/044082A1 (Riddle, et al.):

(R¹O)_(p)—Si(Q¹)_(q)-W—N⁺(R₂)(R₃)—(CH₂)_(m)—Z^(t−)  (I)

wherein:

each R¹ is independently a hydrogen, methyl group, or ethyl group;

each Q¹ is independently selected from hydroxyl, alkyl groups containingfrom 1 to 4 carbon atoms, and alkoxy groups containing from 1 to 4carbon atoms;

each R² and R³ is independently a saturated or unsaturated, straightchain, branched, or cyclic organic group (preferably having 20 carbonsor less), which may be joined together, optionally with atoms of thegroup W, to form a ring;

W is an organic linking group;

Z^(t−) is —SO₃ ⁻, —OPO₃ ²⁻, —PO₃ ²⁻, —OP(═O)(R)O⁻, or a combinationthereof, wherein t is 1 or 2, and R is an aliphatic, aromatic, branched,linear, cyclic, or heterocyclic group (preferably having 20 carbons orless, more preferably R is aliphatic having 20 carbons or less, and evenmore preferably R is methyl, ethyl, propyl, or butyl);

p is an integer of 1 to 3;

m is an integer of 1 to 11;

q is 0 or 1; and

p+q=3.

Suitable examples of zwitterionic silane compounds of Formula (I) aredescribed in U.S. Pat. No. 5,936,703 (Miyazaki et al.), including, forexample:

(CH₃O)₃Si—CH₂CH₂CH₂—N⁺(CH₃)₂—CH₂CH₂CH₂—SO³⁻; and

CH₃ CH₂O)₂Si(CH₃)—CH₂CH₂CH₂—N⁺(CH₃)₂—CH₂CH₂CH₂SO3⁻.

Other examples of suitable zwitterionic silane compounds and theirpreparation are described in U.S. patent application Ser. No. 13/806,056(Gustafson et al.), including, for example:

In some embodiments, a layer of salt material 140 is applied to thesensing element 10 or surface treatment layer 120 of the sensing element10. The layer of salt material 140 may provide for a referenceelectrical property value of the electrode pair A, B. This may be usefulwhen two or more electrode pairs are utilized with the sensing element10. The layer of salt material 140 may be disposed on the high surfaceenergy region 3.

In some embodiments, a layer 130 comprising a hygroscopic material maybe applied to the sensing element 10 or surface treatment layer 120 ofthe sensing element 10, and then allowed to dry. In some of theseembodiments, a layer of salt material 140 may be disposed on or with thehygroscopic material layer 130 within the high surface energy region 3of the sensing element 10. The salt material 140 may mix with thehygroscopic material layer 130 to form a combined hygroscopic materialand salt layer 130, 140.

In some embodiments, a hygroscopic material layer 130 is disposed on thesensing element 10 and is in contact with at least one of layers 11, 120and electrode pair structure 2. FIG. 5B is a flow diagram of the processof FIG. 5A described above with the addition of the hygroscopic materiallayer 130. The sensing element 10 with the surface treatment layer 120of FIG. 5A is then treated with a hygroscopic material solution (forexample, a hygroscopic material solution may be 0.1 wt % sorbitol inwater) at step 260 and heated to 110 degrees Celsius at step 261. Thisillustrative hygroscopic material layer 130 may exist predominantly onthe surface of the electrically non-conductive surface 11 in betweenelectrode pair structure 2 or between at least one pair of electrodes A,B or within the gap 12 or on the surface treatment layer 120. Theillustrative surface treatment layer 130 may define the high surfaceenergy region 3.

In some embodiments, the addition of a hygroscopic material layer 130may be used to modify the hygroscopic properties of a sensing element 10surface to which it is applied and may define the high surface energyregion 3 on the sensing element 10. When used on a surface of a sensingelement 10 that functions based on electrical impedance variations, somehygroscopic materials have the property of altering hygroscopicproperties without contributing mobile ions in solution. Additionally,some hygroscopic materials have another advantageous property of lowvapor pressure. The hygroscopic properties of polyols are due to theirwater activity, which is influenced by presence of a large number ofhydroxyl groups in the molecule. The water activity thermodynamics of avariety of polyol sugar alcohols are described by Compernolle, S. andMuller, J.-F., Atmos. Chem. Phys., 14, 12815-12837 (2014). For example,sorbitol is shown to form a thermodynamically stable water-sorbitolmixture at relative humidity greater than 40%. This property may beadvantageous when the sensing element 10 to be modified functions basedon the ionization of particles in a liquid. The presence of ahygroscopic material, such as a sugar alcohol, on the sensing element 10or surface of the electrically non-conductive surface 11 in betweenelectrode pair structure 2 or between at least one pair of electrodes A,B or within the gap 12 or on the surface treatment layer 120 may enableuse in a wider range of humidity environments.

In certain embodiments, the hygroscopic material layer 130 includescompounds with a plurality of hydroxyl groups. For example, thehygroscopic material layer 130 may be comprised of polyethylene glycolavailable from Sigma-Aldrich, MO, USA. In other suitable examples, thepolyol layer may include at least one sugar alcohol. Some examples ofsuitable sugar alcohols include glycerol, erythritol, arabitol, xylitol,ribitol, mannitol, sorbitol, galactitol, allitol, iditol, maltitol,isomalitol, lactitol, dulcitol, and talito, all available fromSigma-Aldrich, MO, USA. In other suitable examples, the polyol layer 130may include saccharide compounds. Some examples of suitable saccharidesinclude glucose, fructose, galactose, sucrose, lactose, cellulose andstarch available from Sigma-Aldrich, MO, USA.

The thickness of the surface treatment layer 120 or the silane surfacetreatment layer 120 may be any useful thickness. In many embodiments,the surface treatment layer 120 or the silane surface treatment layer120 is less than 50 nanometers, or from 1 to 50 nanometers thick.

When present, the thickness of the hygroscopic material layer 130 may beany useful thickness. In some embodiments, the thickness of thehygroscopic material layer 130 may be from 0.1 to 10 micrometers thick.Thicknesses greater than 10 micrometers or less than 0.1 micrometers maybe useful also. The thickness of the hygroscopic material layer 130 mayimpact the total amount of water absorption, as well as the kinetics ofabsorption. By altering the thickness, which may be accomplished byaltering the coating weight, the sensing element response may beimproved for a given environment. Examples of the impact of thehygroscopic layer thickness is illustrated in FIG. 13A-13D.

The sensing element 10 may omit one or more of the layers describedabove, and the layers may be constructed with a range of coating weightsand thickness combinations, as desired. When used with a sensing element10 that functions based on electrical impedance variations, the silanesurface treatment layer 120 has the property of altering surfaceproperties without contributing significant amounts of mobile ions insolution. In some embodiments, the addition of a hygroscopic materiallayer 130 may be used to modify the hygroscopic properties of sensingelement 10 and assist in defining the high surface energy region 3 onthe sensing element 10. When used with a sensing element 10 thatfunctions based on electrical impedance variations, the hygroscopicmaterial layer 130 may have the property of altering surface propertieswithout contributing significant amounts of mobile ions in solution.

FIG. 4A is a schematic diagram of top, front, and side view of anotherillustrative sensing element 10 having two electrode pair structures 2,4, or two pairs of electrodes A, B and C, D.

The sensing element 10 is configured to interact with an environment ofinterest. The sensing element 10 includes a substrate 1 including anelectrically non-conductive surface 11, two high surface energy regions3, and two electrode pair structures 2, 4 disposed on the electricallynon-conductive surface 11. Each electrode pair structure 2, 4 includesat least one pair of electrodes A, B and C, D having a gap 12 _(AB) and12 _(CD) therebetween. At least a portion of each electrode pairstructure 2, 4 is within the corresponding high surface energy region 3.The high surface energy region 3 may be discontinuous, such that a lowersurface energy region 6 separates the high surface energy region 3corresponding to each electrode pair A, B and C, D, as illustrated. Thesensing element 10 is configured to sense fluid-soluble orfluid-ionizable particulate matter. A conductive region 5 mayelectrically connect the electrode pair structure 2, 4 with sensingelectronics. This electrode configuration may be referred to asincluding four electrodes A, B, C, and D where two pairs of electrodesare formed A-B and C-D.

The low surface energy region 6 may assist in keeping liquid in each ofthe two high surface energy regions 3 separate from each other. Regionsoutside of the perimeter of the high surface energy regions 3 may have alower surface energy than the surface energy within the perimeter of thehigh surface energy regions 3. Thus, liquid vapor or water vapor mayselectively condense and form a liquid layer or liquid volume thatremain within the perimeter of the high surface energy regions 3.

Water vapor may be produced by human breath inside of a respirator, suchas a filtering facepiece respirator (FFR), or elastomeric respirator,for example. This water vapor may condense onto the high surface energyregion 3 of the sensing element. In an example, salt aerosol particles,such as sodium chloride, may come into contact with this condensed watervapor so that the salt particle dissolves and alters an electricalproperty (for example, impedance) of at least one of the electrode pairsA, B and C, D. The spatially separated surface treatments enabledistinctly separate signals by preventing molecular migration betweenthe electrode pair structures 2 and 4.

In some embodiments, at least a portion of a region surrounding at leastone of the electrode pair structures 2, 4 may have a particulate or saltmaterial predisposed on the electrode pair structure 2 or 4 or withinthe gap 12 _(AB) or 12 _(CD) therebetween (as illustrated in FIG. 3).For example, sodium chloride may be predisposed on a surface surroundingan electrode pair structures 2, or 4 or within the gap 12 _(AB), or 12_(CD) to generate an electrical impedance related to the quantity ofpredisposed sodium chloride. This may be referred to as a referenceelectrode. The solid material (sodium chloride, for example) may bedisposed or provided within the perimeter of one high surface energyregion 3 in a known amount. Once water vapor condenses on this highsurface energy region 3 the known amount of solid material (sodiumchloride, for example) is dissolved and may provide a referenceelectrical property or reference electrode (electrode pair structure 2or 4) that a sensing electrode (remaining electrode of 2 or 4) may becompared to during testing or the sensing operation.

FIG. 4B is a schematic diagram of top, front, and side view of anotherillustrative sensing element 10.

The sensing element 10 is configured to interact with an environment ofinterest. The sensing element 10 includes a substrate 1 comprising anelectrically non-conductive surface 11, two high surface energy regions3, and two electrode pair structures 2, 4 disposed on the electricallynon-conductive surface 11. Each electrode pair structure 2, 4 includesone electrode and share a common electrode C and having a gap 12 _(AC),12 _(BC) therebetween. At least a portion of each electrode pairstructure 2, 4 is within the corresponding high surface energy region 3.The sensing element 10 is configured to sense fluid-soluble particulatematter. A low surface energy region 6 may separate the two high surfaceenergy regions 3. A conductive region 5 may electrically connect theelectrode pair structure 2, 4 with sensing electronics. This electrodeconfiguration may be referred to as comprising three electrodes A, B,and C where two pairs of electrodes are formed A-C and B—C and whereelectrode C is common to both electrode pairs.

The sensing element may be configured to be electrically coupled ordecoupled to one or more additional electronic elements by a physicalproximity to one or more electronic elements. In some embodiments, forexample, an electrically conducting region 5 may be configured forphysical contact with an electronic element in a connector. In someembodiments, for example, an electrically conducting region 5 may beconfigured to electrically couple with another electronic elementwithout physical contact via a time-varying electromagnetic field.

FIG. 6 is a schematic diagram cross-sectional view of the sensingelement 10 of FIG. 4A illustrating fluid 9 disposed on the electrodepair structures 2, 4. The sensing element 10 includes a substrate 1including an electrically non-conductive surface 11, two high surfaceenergy regions 3, and two electrode pair structures 2, 4 disposed on theelectrically non-conductive surface 11. Each electrode pair structure 2,4 includes at least one pair of electrodes A, B, and C, D having a gap12 _(AB) and 12 _(CD) therebetween. At least a portion of each electrodepair structure 2, 4 is within the corresponding high surface energyregion 3. The sensing element 10 is configured to sense fluid-solubleparticulate matter. A low surface energy region 6 may separate the twohigh surface energy regions 3. The configuration of the high surfaceenergy regions 3 enables the selective condensation of water or liquidvapor onto these high surface energy regions 3 to form the liquidbubbles, or liquid layers, or liquid volumes 9.

In embodiments with multiple electrode pairs A, B, and C, D, the regionsof different surface energies may be configured such that fluid 9, asillustrated in an example in FIG. 6, preferentially wets the highsurface energy regions 3 surrounding at least one of the electrode pairsA, B, or C, D, but the fluid 9 does not make fluid contact with theother electrode pair A, B, or C, D. The preferential separation of fluidcontact with the different electrode pairs is shown in FIG. 6, wherefluid 9 preferentially wets the regions proximal to the two electrodepairs 2 and 4, but does not form a fluid bridge between the pairs A, B,and C, D, due to the low surface energy region 6. Liquid or water 9 hasa lower affinity to wet region 6, producing multiple distinct fluidregions 9 that are not in fluid communication with one another.

FIG. 7 is a schematic diagram cross-sectional view of an illustrativesensing element 10 with a filtering element 7. FIG. 8 is a schematicdiagram cross-sectional view of the sensing element of FIG. 7illustrating fluid 9 disposed on the electrode pair structures 2, 4.

The filtering element 7 may be configured such that it prevents at leastsome particles or a component from the environment from contacting atleast one electrode pair C, D. In some embodiments, the particulatefilter 7 may be a nonwoven filter element. In some embodiments, astandoff material 8 is disposed on the electrically non-conductivesurface 11, such that the material 8 surrounds at least a portion of anelectrode pair structure 4, and the filter material 7 is disposed on thestandoff material 8 such that the filter material 7 is configured to notphysically contact the electrode pair C, D.

One suitable example of a standoff material 8 is an adhesive foamcommercially available under the trade designation “3M Urethane FoamTape 4056” from 3M Co., MN, USA, for example. The standoff material 8 orfoam may have an ionic content of less than 1000 ppm, such that theextraction of ions by a condensed fluid is minimized. The standoffmaterial 8 may also have intrinsic properties to add or remove chemicalconstituents to the liquid layer. For example, the standoff material 8may be a desiccant to remove some water from the liquid layer. As anexample, this configuration may result in a reference electrode pair C,D, that may interact with gaseous compounds in the environment which areable to pass through the filter material 7. However, at least someparticles are intercepted by the filter material 7 and are preventedfrom interacting with the reference electrode pair C, D.

The filtering element 7 may provide the only airflow communication withthe electrode pair structure 4 or electrode pair C, D and thesurrounding environment, but does not provide particulate communicationwith the electrode and the surrounding environment. Thus, the electrodepair structure 4 may operate as a real-time reference electrode that mayremove environmental effects from the sensing signal of the sensingelectrode pair structure 2 or electrode pair A, B (not protected by thefiltering element 7), for example. In other embodiments, a fixed amountof solid material of interest, such as salt 140 (see FIG. 3) or sodiumchloride, may be disposed on the reference electrode pair structure 4 orelectrode pair C, D and contained by the filtering element 7. Thisconfiguration may provide a reference electrode pair or electrode pairstructure 4 or electrode pair C, D that has a set signal to the sensingelectronics for comparison with the sensing electrode pair or structure2 or electrode pair A, B (not protected by the filtering element 7).

FIG. 9 is a schematic diagram of the top view of another illustrativesensing element 10. The sensing element 10 includes a substrate 1comprising an electrically non-conductive surface 11, two high surfaceenergy regions 3, and two electrode pair structures 2, 4 disposed on theelectrically non-conductive surface 11. Each electrode pair structure 2,4 includes at least one pair of electrodes A, B and C, D having a gap 12_(AB) and 12 _(CD) therebetween. At least a portion of each electrodepair structure 2, 4 is within the corresponding high surface energyregion 3. The sensing element 10 is configured to sense fluid-solubleparticulate matter. A low surface energy region 6 may separate the twohigh surface energy regions 3. Here one electrode pair A, B is betweenthe other electrode pair C, D. The inner electrode pair C, D is shown aslinear, parallel and co-extending, however, the inner electrode pair C,D may be interdigitated as described above.

FIG. 10 is a schematic diagram of the top view of another illustrativesensing element 10. The sensing element 10 includes a substrate 1comprising an electrically non-conductive surface 11, one high surfaceenergy region 3, and one electrode pair structure 2 disposed on theelectrically non-conductive surface 11. The electrode pair structure 2includes at least one pair of electrodes A, B having a gap 12therebetween. At least a portion of each electrode pair structure 2 iswithin the high surface energy region 3. The sensing element 10 isconfigured to sense fluid-soluble particulate matter. A low surfaceenergy region 6 may surround or circumscribe the high surface energyregion 3. The electrode pair A, B is shown as linear, parallel andco-extending, however, the electrode pair A, B may be interdigitated asdescribed above. One or more perforations, holes, or apertures 15 extendthrough the substrate 1. The perforations, holes, or apertures 15 mayprovide for air flow communication through the sensing element 10 andmay improve particle contact with the sensing element 10 or improve thefluid dynamics of the fluid near the electrode pair A, B.

A protective film or removable liner (not shown) may be removablyadhered to the sensing element 10 to provide protection during transportand installation of the sensing element 10 and electrode pair structures2, 4. The sensing element 10 is inserted into the sensor, which may beapplied to a respirator or personal protective device or element, asdescribed below.

Referring now to FIGS. 19-21, in some embodiments, an electrical bridge306 is disposed on a surface of the sensing element 10. The electricalbridge 306 is configured to modify an electrical conduction path in theelectric circuit 100. In an exemplary embodiment, when the sensingelement 10 is inserted into the plug 105, the electrical bridge 306modifies the power circuit of the electronic meter 100 from an opencircuit to a closed circuit, or from a high resistance circuit to a lowresistance circuit, allowing the flow of increased electrical current,or presenting a voltage, to the circuit element. In another example, theelectrical bridge 306 completes the circuit to a voltage regulator onthe electric circuit 100. In another example, the electrical bridge 306modifies the input to a controller which enables a high power state. Forexample, insertion of the sensing element 10 having the electricalbridge 306 may cause the electronic sensor to change from a low powerstate with an average power consumption X (for example, X<100microwatts) to a high power state Y with a power consumption greaterthan ten times A (for example, Y>10X=1 milliwatt). This feature may beuseful as a means of conserving battery power, as it configures thecircuit to only consume power while the sensing element 10 is pluggedinto the sensor 320. It is to be understood that the sensing element 10may be made to function with any combination or omission of previouslydescribed features, depending on the application.

Referring now to FIG. 32, in some embodiments, the sensing element 10may comprise one or more heating elements 321 a, 322 a in electricalcommunication with one or more pairs of contacts 321, 322. The heatingelements 321 a, 322 a may be in the same plane as the one or moreelectrode pairs 301 a, 302 a, or may be in a different plane. Forexample, the one or more heating elements 321 a, 322 a may be on theopposite side of sensing element 10. In some embodiments, the one ormore heating elements 321 a, 322 a may be covered by an electricallyinsulating layer such they are prevented from forming electricalcommunication with any condensed fluid. For example, the heatingelements 321 a, 322 a may be configured to increase the temperature ofthe detection surface (not shown) of a sensing element 10 so as toincrease the vapor pressure of fluid condensed on the sensing element10. In some embodiments the electrical bridge 306 may be in the sameplane as the one or more heating elements.

FIG. 15 is a schematic diagram of an illustrative respirator sensorsystem 300. The system 300 includes a respirator 310, a sensor 320including a sensing element (as described herein), and a reader 330configured to be in wireless communication with the sensor 320. Thesensor 320 is positioned substantially within an interior gas space ofthe respirator, or mounted substantially on the exterior surface of therespirator 310.

The respirator sensor system 300 may be configured to detect thepresence of unfiltered air within the interior gas space of therespirator 310.

As described above, the sensing element is configured to sensefluid-soluble particulate matter when a liquid layer is disposed in agap on at least a part of the surface of the sensing element. Fluidionizable particles may at least partially dissolve and may at leastpartially ionize in the liquid layer, resulting in a change in anelectrical property between at least two of the electrodes.

Water vapor may be produced by human breath inside of the respirator andcondense onto the high surface energy region of the sensing element andform the liquid layer. In an example, salt aerosol particles, such assodium chloride, may come into contact with this condensed water vaporso that the salt particle dissolves and alters an electrical property(for example, impedance) of at least one of the electrode pairs. Thischange in electrical property may be sensed by the sensor 320 andwirelessly communicated to a remote reader 330. The transport of thefluid ionizable particulate matter to the sensing element may beeffected by human breath. In some embodiments, the transport of thefluid ionizable particulate matter to the sensing element may beconducted by using a gas-moving element. In some embodiments, thegas-moving element is a fan or pump.

The sensing element is a fluid ionizable detection element that may beconfigured such that the condensing vapor does not condense uniformly onthe surface of the sensing element, as described above. The fluidionizable detection element may be further configured such that thecondensed vapor in contact with at least one electrode does not form acontinuous condensed phase to at least one other electrode.

The respirator 310 may be any personal protective respirator articlesuch as a filtering facepiece respirator or elastomeric respirator, forexample. The sensor 320 may include a power source, communicationinterface, sensing electronics, and antenna. The sensor 320 power sourcemay be a battery, a rechargeable battery, or energy harvester.

The sensing element may be configured to be replaceable and mechanicallyseparable from the sensor 320. The sensing element may be in removablecommunication with the sensor 320. The sensing element may be inwireless communication with the sensor 320. The sensor 320 may bereusable by replacing a used or spent sensing element with a fresh ornew sensing element.

The sensor 320 may be fixed to, or adhered to, or connected to aninterior surface of the respirator 310 or personal protective device orelement. The interior surface may define an interior gas space of therespirator once the respirator 310 or personal protective device orelement is worn by a user. The interior gas space is in airflowcommunication with the breath of the user wearing the respirator 310 orpersonal protective device or element. In some embodiments, the sensor320 may be removably positioned or attached within the interior gasspace. In some embodiments, the sensor 320 may be removably positionedor attached to the interior surface of the respirator 310. In someembodiments, the sensor 320 may be removably positioned or attached toan exterior surface of the respirator 310. The sensor 320 may be fixedto, or adhered to, or connected to an interior surface or an exteriorsurface of the respirator 310 by any useful attachment system, such as,adhesive, hook and loop, friction fit connector, or suction, forexample. For example, the sensor 320 may attach to an exterior surfaceof the respirator by way of a port (not shown) in the respirator whichcreates a fluid channel between the interior gas space of the respiratorand the exterior gas space. For example, the sensor 320 may be coupledto such a port by pressing the sensor 320 to the port, i.e. a frictionfit connection.

The size and weight of the sensor 320 are selected such that the sensordoes not interfere with a wearer's use of the respirator 310. The sizeof the sensor 320 and a weight of the sensor 320 are selected such thatthe sensor 320 does not alter the fit the respirator 310 on a wearer.The sensor 320 may have a weight in a range from 0.1 to 225 grams,preferably less than 10 grams, or from 1 to 10 grams. A sensor weighing225 grams may not alter the fit of the respirator if the respirator issufficiently tight, but lower weights are preferred so as to reduce theweight of the respirator. The sensor 320 may have a volume in a rangefrom 0.1 to 50 cm³, preferably less than 10 cm³, or from 1 to 10 cm³.

Referring now to FIG. 18, the sensor 320 shown includes electric circuit100, which comprises a plurality of electrical contacts 104, and agas-moving element 200. The electric circuit 100 is configured tomeasure at least one electrical characteristic (e.g. impedance) betweenat least one pair of electrical contacts 104. The sensor 320 isconfigured to accept a sensing element 10 into a plug 105 as shown inFIG. 19, where the plug contains the electrical contacts 104. In someembodiments, the gas-moving element 200 is a fan, such as an axial fanor a centrifugal (i.e. blower) fan. Some suitable examples of fans arethe Mighty Mini series commercially available from Sunonwealth ElectricMachine Industry Co., Ltd, which range in size from 9 mm×9 mm×3 mm to 30mm×30 mm×3 mm. In other embodiments, the gas-moving element 200 is apump, such as a piezoelectric pump.

In some embodiments, the sensing element 10 is configured to bemechanically separable from the other elements of the sensor 320. Thisfeature is useful if the sensing element 10 is configured to bedisposable, or interchangeable. In some embodiments, the reader 330comprises a plug 105 that contains electrical contacts into which thesensing element 10 may be inserted, where the mechanical mating of thesensing element 10 and the plug 105, which results in electricalconnection between the sensing element 10 and the electrical contacts104, creates an electrical connection between the sensing element 10 andthe electric circuit 100.

In some embodiments, it is advantageous to contain the sensing element10 within a gas transport structure 400, wherein the gas transport isdriven by the gas-moving element 200, as shown in FIG. 22. The gastransport structure 400 serves to direct a predetermined flow rate ofgas in a controlled manner to the detection surface 301 a and optionaladditional detection surfaces. In some embodiments, an exhaust channel405 is aligned with the exhaust outflow of the gas-moving element 200such that gas may be exhausted out of the gas transport structure 400.In this embodiment, the sensing element 10 is arranged upstream of thegas-moving element 200. Still further upstream, one or more gas intakechannels 401, 402 are arranged such that gas may enter through the gasintake channels, be directed towards the detection surface 301 a of thesensing element 10, and then exhausted through exhaust channel 405. Insome embodiments, detection surface 301 a of the sensing element 10 islocated substantially perpendicular to the predetermined flow of gas.This arrangement of the one or more gas intake channels 401, 402,sensing element 10, and gas-moving element 200 may result inimprovements in sensor response time and sensitivity to changes inaerosol concentration over alternative arrangements, due to the rapidand controlled manner by which this combination of elements movessamples to the detection surface 301 a of the sensing element 10. Forexample, when used as part of a respirator fit test, this arrangementmay result in rapid detection of changes in respirator fit at specificinstances in time during a fit test. This may enable more preciseidentification of specific actions that result in changes in respiratorfit for the wearer.

In some embodiments, where the sensor 320 is configured to detect anaerosol, the gas transport structure 400 is constructed as an aerosolimpactor where the sensing element 10 serves as the impactor plate. Thenature of an impactor is that they preferentially collect only particleslarger than a given size on the impactor plate. Hence, in this example,the combination of elements 400 and 10 results in the preferentialcollection of particles larger than a given size, such as 1 microndiameter or 2.5 microns diameter or 10 microns diameter, onto thesensing element 10. FIG. 23 shows one example of a suitable internalstructure of the gas transport structure 400, with one example sensingelement 10 in an inserted state. Gas-moving element 200 is not shown inthis figure for purposes of clarity, but it should be assumed to beplaced as described previously—within the gas transport structure 400,in between the exhaust channel 405 and the sensing element 10. In FIG.23, the exhaust channel 405 is configured for an axial fan, whereas inFIG. 22, the exhaust channel 405 is configured for a centrifugal fan.While they impart different properties on the system, it is understoodthat either configuration can be made suitable.

In some embodiments, the gas transport structure 400 contains aplurality of channels in order to accept a plurality of sensing elementsbetween the intake channels and the exhaust channels. This alsonecessitates the inclusion of multiple plugs 105 into which each elementmay insert. In this embodiment, the air that passes over one sensorstrip subsequently passes over a second sensor strip. This approachmimics the design of a cascade impactor whereby subsequent stagescollect successively smaller particles.

In some embodiments, the electric circuit 100 and the gas-moving element200 are powered by a power source, such as a battery, 106 which is partof the sensor 320, as shown in FIG. 24. In some embodiments, the powersource 106 is a primary battery which is configured to be replaced. Insome embodiments, the power source 106 is a rechargeable battery. Forexample, a 3.7 V lithium ion battery with a 40 milliamp-hour capacitymay power a fan at 2.5 V and 30 mA, plus the meter electronics, forgreater than one hour of continuous run time is useful in the presentdisclosure. Those skilled in the art will recognize that different sizedbatteries may be used for applications requiring differing run times orpower requirements. Smaller batteries have the benefit of smaller sizesand lower masses. A rechargeable battery requires a means of chargingthe battery. In some embodiments, a plug 107 may be configured toreceive a charging electrical cable, such as a micro-USB cable, tocharge the battery. In some embodiments, the electric circuit 100 maycomprise an inductive charging structure such that the battery may becharged wirelessly. An inductive charging structure reduces the numberof openings that must remain accessible to the circuit, thereby reducingthe risk of the introduction of environmental contaminants to thecircuit.

In some embodiments, the presently disclosed sensor 320 includes ahousing 410 that has an opening configured to receive the sensingelement 10; an electric circuit 100 operably connected to the housing410, where the electric circuit 100 is configured to detect at least onecharacteristic of electrical impedance across at least one pair ofelectrodes; at least one gas-moving element 200 in electricalcommunication with the electric circuit 100; and a reader 330 incommunication with the electric circuit 100, where the reader 330 isconfigured to compare information about a gas volume external to thehousing 410 with information about a gas volume within the housing 410.In some embodiments, a housing 410 is configured such that the electriccircuit 100 and the previously described gas transport structure 400 arecontained within the housing 410, as shown in FIG. 25. In someembodiments, the gas transport structure 400 is mechanically separablefrom the housing 410. In some embodiments, the sensing element 10 has acertain 3 d shape, such as rectangle, cube, cylinder, irregular 3 dshape, and the like. The housing 410 may include an opening to receivethe sensing element 10, where the shape of the opening complements theshape of the sensing element 10. For example, the opening may berectangular shape. This results in the that, when the sensing element 10is inserted in the opening, wherein, when the sensing element 10 isinserted in the opening, there is substantially no fluid communicationfrom the outside of the housing 410 to the inside of the housing throughthe interstitial space between the opening and the sensing element 10.

In some embodiments, the electric circuit 100 is affixed to the housing410. For example, in some instances, the electric circuit 100 is affixedto at least one interior wall of the housing 410.

In some embodiments, it is advantageous for the sensing element 10 tocomprise a tab 305 as shown in FIG. 26, which may be used to assist inremoval of the sensing element 10 from the sensor 320 (see FIGS. 27 and28 for examples of removal and insertion). In some embodiments, thesystem may include a sensing element ejector mechanism to assist withremoval of the sensing element 10 from the housing 410.

In some embodiments, one or more gas channels 404 may be disposed on asurface of housing 410 as shown in FIG. 28, such that gas may enter thegas channel 404 before passing through gas intake channels 401, 402. Insome embodiments, the housing 410 may be comprised of several pieces,such that pieces 411 may be removed to access internal components, asshown in FIG. 29.

In some embodiments, a transport control structure 407 is disposed inproximity to the exhaust channel 405 as shown in FIG. 30, such that gasmust pass through the transport control structure 407 when movingbetween the exhaust channel 405 and the surrounding medium. Thetransport control structure may provide benefits by controlling thebackwards flow of analytes from the surrounding medium into exhaustchannel 405 and then into the sensor housing. In some embodiments, thetransport control structure 407 is a particulate filter. The particulatefilter may provide benefits of preventing particulates from entering thesystem through the exhaust channel 405. In some embodiments, thetransport control structure 407 is a gas filter. The gas filter mayprovide benefits of preventing certain gas molecules from entering thesystem through the exhaust channel 405. In another embodiment, the gascontrol structure 407 is a valve, such that gas is allowed to pass fromexhaust channel 405 to the surrounding medium, but is impeded fromflowing in the other direction.

In some embodiments, the presently disclosed sensor 320 includes aheating element and related electrical components so as to optionallyprovide heat to one or more locations in the housing 410. For example,the heating element may be disposed in close proximity to a locationoccupied by sensing element 10 when the sensing element is inserted intothe housing 410. For example, the heating element may be configured toincrease the temperature of a detection surface of a sensing element 10so as to increase the vapor pressure of fluid condensed on the sensingelement. For example, the heating element may promote evaporation ofcondensed water from electrical impedance sensing element, or thesurface of optical sensing elements.

The sensor 320 comprises elements which enable practical operation ofthe sensor 320 without a need for physical connection to elements thatwould expand the device beyond a certain size, such as 20 cm³,including: a power circuit, where the power may be provided by anelement in the sensor itself, such as a battery, or by wireless means,such as inductive power; an electrical characteristic analysis circuitin electrical communication with electrical contacts 104, and amicrocontroller, both in communication with a power circuit; anair-moving element in electrical communication with a power circuit; anda data transmitting structure. The data transmitting structure may be awireless communications circuit, such as radio frequency, near fieldcoupling, WiFi, or Bluetooth. In some embodiments, the data transmittingstructure may be a data memory storage structure. In some embodiments,the data transmitting structure may be a visual, audible, or hapticindicator, such as a light emitting diode, audible alarm, or vibratingalarm.

Use of the sensor in some applications may enable improvements in theprecision, accuracy, sensitivity and response time of the detection ofgas and/or aerosol particles within a respirator. Examples of sodiumchloride aerosol detection data by a sensor of the type described herewhen mounted substantially within the interior gas space of a respiratorcompared to a sodium flame photometer are shown in FIGS. 31A-D. A sodiumflame photometer is a device used to measure sodium-containing aerosolby running sample of the aerosol through a hydrogen flame and measuringthe optical emission. In these examples, the data is collectedsimultaneously, with the sensor placed entirely within the breathingspace of the respirator, and the sodium flame photometer samplingthrough a port made in the respirator. Examples of sodium chlorideaerosol detection data by a sensor of the type described here whenmounted on an external surface of a respirator compared to a sodiumflame are shown in FIGS. 33A-D. In these examples, the data is collectedsimultaneously, with the sensor mounted on the exterior surface of therespirator via connection to a port on the respirator, and the sodiumflame photometer sampling through a port made in the respirator

In some embodiments, the sensor 320 may wirelessly communicate with aremote reader 330. The sensor 320 may wirelessly communicate data to thereader 330 regarding changes in an electrical property of the sensingelement. In some embodiments, the communication between the reader 330and the sensor 320 is via electromagnetic communication, such as viamagnetic field, or Near Field Communication, or Bluetooth Low Energy, oroptical illumination and detection, WiFi, Zigbee, or the like. In someembodiments, the sensor 320 may communicate via a wired connection tothe reader 330, such as being on the same electrical circuit as thereader 330.

The sensor 320 may and reader 330 may communicate with one another aboutone or more constituents of a gas or aerosol within the interior gasspace. The sensor 320 may and reader 330 may communicate with oneanother about physical properties related to a gas within the interiorgas space, such as temperature, pressure, humidity, and the like. Thesensor 320 and reader 330 may communicate with one another aboutparameters used to assess the performance of exercises by a wearer ofthe respirator, such as vigor of breathing and/or bodily motion. Forexample, the sensor 320 may comprise force sensors, such asaccelerometers, which provide signals related to the motion of thewearer's head when the sensor is mounted within or on the respiratorworn by the wearer. For example, the sensor 320 may comprise sensorsthat provide signals related to the vigor of breathing of the wearer,such as temperature sensors, humidity sensors, air flow sensor, pressuresensors, and the like. For example, exercises useful in the presentdisclosure include those prescribed by US Occupational Safety and HealthAdministration in 30 CFR 1910.134 Appendix A. An example of sensorsignals from these exercises is shown in FIG. 34.

The reader 330 may include a power source, communication interface,control electronics, and antenna. The reader 330 may wirelesslycommunicate with a remote device 350 via the internet 340 as shown inFIG. 15. The reader 330 may communicate with the internet 340 viawireless connection. The reader 330 may communicate with the internet340 via direct wired communication. The remote device 350 may includeany of memory, data storage, control software, or at least one processorto receive and utilize the data or information provided by the reader330 directly or via the internet 340.

The respirator sensor system 300 may be utilized to detect fluidionizable particles in a gaseous medium. The method includes contactinga gaseous medium with a fluid ionizable particulate matter sensingelement, and condensing a component of the gaseous medium on at least aportion of the fluid ionizable particulate matter sensing element; anddetermining an electrical property at a first point in time between apair of electrodes of the fluid ionizable particulate matter detectionelement; and determining an electrical property at a second point intime between a pair of electrodes of the fluid ionizable particulatematter detection element; and determining a value related to thepresence of fluid ionizable particles in the gaseous medium at leastpartially by comparing the value of the electrical property at the firstpoint in time to the electrical property at the second point in time.

The respirator sensor system 300 may be utilized to detect fluidionizable particles in a gaseous medium. The method includes contactinga gaseous medium with a fluid ionizable particulate matter sensingelement, and condensing a component of the gaseous medium on at least aportion of the fluid ionizable particulate matter sensing element; anddetermining an electrical property at a first frequency, such as 1 Hz,between a pair of electrodes of the fluid ionizable particulate matterdetection element; and determining an electrical property at a secondfrequency, such as 100 kHz, between a pair of electrodes of the fluidionizable particulate matter detection element; and determining a valuerelated to the presence of fluid ionizable particles in the gaseousmedium at least partially by comparing the value of the electricalproperty at the first frequency to the electrical property at the secondfrequency. The frequency may include DC.

The respirator sensor system 300 may include an additional computingsystem or remote device 350 wherein data is communicated between therespirator sensor system 300 and the additional computing system orremote device 350. In some embodiments, the additional computing systemis a cloud computing architecture. The communication between the reader330 and the additional computing system or remote device 350 may be viaa wired connection or via wireless internet network. The additionalcomputing system or remote device 350 may record data transmitted by thereader 330. The additional computing system or remote device 350 mayprocess data transmitted by the reader 330, and communicate informationback to the reader 330.

The respirator sensor system 300 may be utilized to detect fluidionizable particles in a gaseous medium. The method includes contactinga gaseous medium with a fluid ionizable particulate matter sensingelement, and condensing a component of the gaseous medium on at least aportion of the fluid ionizable particulate matter sensing element; anddetermining an electrical property between a first pair of electrodes ofthe fluid ionizable particulate matter detection element; anddetermining an electrical property between a second pair of electrodesof the fluid ionizable particulate matter detection element; anddetermining a value related to the presence of fluid ionizable particlesin the gaseous medium at least partially by comparing the value of theelectrical property of the first pair of electrodes to the electricalproperty of the second pair of electrodes.

The method may include the second pair of electrodes utilized as areference electrode. The reference electrode may be an analyte referenceelectrode. The reference electrode may be isolated from a targetcomponent of the gaseous medium. The target component of the gaseousmedium may be a fluid ionizable particle, such as a salt, for example.The respirator sensor system 300 may be utilized to provide real-timefeedback on the quality of the respirator fit. The respirator sensorsystem 300 may be utilized to provide a method of fit testing. The fittesting method includes providing a respirator 310, then providing asensor 320 including a sensing element removably positionedsubstantially within an interior gas space of the respirator, thenproviding a reader 330 configured to be in wireless communication withthe sensor 320; and positioning the respirator 310 over a mouth and anose of a user while the sensor 320 is positioned substantially withinan interior gas space of the respirator; and observing respirator fitassessment data communicated from the reader 330 based on informationfrom the sensor 320.

In some embodiments, the fit testing method as shown in FIG. 16Aincludes the steps of providing a respirator 1000 donned by a wearer2000; providing an aerosol generator 3000 with a known aerosol outputparameter 5000; providing an enclosure 4000 that is physically supportedaround the wearer's head 2001, wherein the aerosol generator 3000delivers aerosol with the known aerosol parameter 5000 that is at leastpartially contained within the enclosure 4000 around the wearer's head2001 and the enclosure 4000 at least partially contains the aerosol 5000around the wearer's head 2001; providing a sensor 6000 comprising asensing element operably connected to the respirator 1000, wherein thesensor 6000 is configured to monitor a particulate concentrationparameter within the respirator 1000; providing a reader configured tocommunicate with the sensor 6000, wherein the reader is configured toprovide a respirator fit parameter based on a comparison of theparticulate concentration parameter to the known aerosol outputparameter 5000. In some embodiments, the enclosure used in this methodis optional as shown in FIG. 16B.

In some embodiments, the sensor 6000 is mounted substantially on anexterior surface of the respirator 1000. In some embodiments, a size ofthe sensor 6000 and a weight of the sensor 6000 are selected such thatthe sensor 6000 does not interfere with a wearer's use of the respirator1000. In some embodiments, a size of the sensor 6000 and a weight of thesensor 6000 are selected such that the sensor 6000 not alter the fit ofthe respirator 1000 on a wearer 2000.

In some embodiments, the reader is integrally connected to the sensor6000. In some embodiments, the reader communicates with the sensor 6000using electromagnetic communication, such as via magnetic field, or NearField Communication, or Bluetooth Low Energy, or optical illuminationand detection, WiFi, Zigbee, or the like.

In some embodiments, this method is an improvement because it provides arespirator fit test or assessment, based on electronic measurements ofgas, aerosol, or particulates leaking into a respirator 1000, whilerequiring only one measurement location (i.e. inside the respirator).Existing methods of this type require a measurement of both the gas,aerosol or particulate matter inside the respirator, and also the gas,aerosol or particulate matter outside the respirator, for everyrespirator fit test or assessment. Requiring only a single measurementlocation reduces the cost and complexity of the test. The ability tomake a fit assessment with only measurements of gas, aerosol orparticulate inside the respirator 1000 enables the use of a relativelyportable fit test system, including an aerosol generator with a knownoutput. These two elements combine to create a system wherein theaerosol concentration surrounding the respirator during the fit test canreliably be made to fall within a predefined range. Because that rangeis predefined, it does not need to be measured during the test, and thefit assessment can be made by only measuring the particulates that leakinto the respirator during the test, and comparing the measurement ofthose particles to the known predefined range of particle concentrationoutside of the respirator.

In another embodiment, a fit testing method as shown in FIG. 17 includesthe steps of: providing a respirator 1000 donned by a wearer 2000;providing a sensor 6000 comprising a sensing element, wherein the sensor6000 is attached substantially inside the respirator 1000 such that aweight of the sensor 6000 is substantially supported by the respirator1000, and wherein the sensor 6000 is configured to monitor a particulateconcentration parameter within the respirator 8000; providing a sensor6100 mounted substantially on an exterior surface of the respirator 1000and configured to monitor a particulate concentration parameter outsidethe respirator 8100; providing a reader configured to communicate withthe sensors 6000 and 6100, wherein the reader is configured to provide arespirator fit parameter based on a comparison of the particulateconcentration within the respirator 8000 to the particulateconcentration parameter outside the respirator 8100. In someembodiments, considering also FIG. 16A, this method further utilizes anenclosure 4000 that is physically supported around the wearer's head2001, wherein the aerosol generator 3000 provides the known aerosolparameter 5000 at least partially contained within the enclosure 4000around the wearer's head 2001 and the enclosure 4000 at least partiallycontains the aerosol 5000 around the wearer's head 2001.

This method is an improvement because it uses a sensor to monitor theparticulates leaking in the respirator that is mounted directly to therespirator. Conventional techniques require the attachment of a lengthytube to the respirator, which provides a fluid path to a sensor mountedin a location apart from the respirator (e.g. a tabletop, or abelt-mount). This requirement is because the sensors used are too largeand heavy to be able to be mounted directly to a respirator withoutsubstantially impacting the fit of the respirator. Sensors useful in thepresent disclosure are small enough (e.g. less than 20 cm³ volume ande.g. less than 25 grams weight) such that they can be mounted directlyto the respirator without impacting the fit of the respirator, orotherwise causing discomfort the wearer.

The respirator sensor system 300 may be utilized to evaluate the fit ofa respirator 310. The method includes: 1) A test subject dons arespirator to which a sensor 320 has been attached within the interiorgas space of the respirator or to an external surface of the respirator310. 2) The test subject enters a contained volume into which saltparticles are injected. The contained volume may be a hood that fitsover the test subject's head or it may be a chamber that a subject stepsinto or any structure that can contain a test subject and a salt aerosolatmosphere. The salt particles may be produced by spray atomization of asolution of water containing a salt such as sodium chloride at aconcentration, for example, of 5 wt %. 3) The test subject performs avariety of exercises such as those described in fit test methodsaccepted by the US Occupational Safety and Health Administration in 30CFR 1910.134 Appendix A. 4) Continuously throughout the test, sensor 320may transmits data to the reader 330 regarding the resistance,capacitance, or other AC impedance properties of the sensing element andreference electrode. 5) Software contained within the reader 330 orother computing device 350 evaluates the data to assess the fit of therespirator on the test subject.

In any of the foregoing methods, the aerosol output parameter is definedby particle concentration, and sometimes additionally average size ofthe particles (e.g., a count median diameter between 0.5 and 2.5micrometers and a geometric standard deviation less than 2.5). In any ofthe foregoing methods, in some embodiments, the particulateconcentration parameter is a measurement of the mass of particlesdissolved in a fluid on a surface of the sensor. In some embodiments,the particulate concentration parameter is a measurement of particlecount within the respirator using, for example, an optical sensor,charge counting mechanism, and the like.

In any of the foregoing methods, the term “supported around the wearer'shead” includes that the enclosure is supported by the wearer's headand/or shoulders, such as, for example, by supports that allow theenclosure to be operably connected to the wearer's head and/orshoulders. In some embodiments, the respirator fit parameter is anindication of how well the respirator fits on a wearer's face. In someembodiments, the respirator fit parameter is defined as a percent volumeof air entering a respirator that is filtered air versus unfiltered air.For example, in some embodiments, the respirator fit parameter isdefined as the ratio of an average particle concentration outside of therespirator divided by an average particle concentration inside therespirator over a period of time. A respirator fit parameter may bedefined as an average, such as an arithmetic average, a geometricaverage, or a harmonic average, of multiple respirator fit parametersmeasured during different time periods. For example, it may be desirablethat a respirator fit parameter is greater than 40, or greater than 100,or greater than 500.

In any of the foregoing embodiments, the reader 330 may be an integratedpart of the sensor 320 and the electric circuit 100, such that any ofthe functions of data processing, comparison of values, data storage,communication, alerts, indication of values, indication of respiratorfit assessment, and any other useful function of a reader as describedherein may be carried out by the sensor without the need forcommunication to any other device.

The respirator sensor system 300 may be utilized with a computer visiontool or camera to assure a consistent quality of the respirator fit. Themethod includes: 1) The respirator wearer undergoes respirator fittesting while standing in front of a camera. The fit test is conductedwith the selected respirator model equipped with wireless aerosol sensordescribed herein. 2) The sensor measures aerosol leakage into therespirator in real time as the worker adjusts the respirator to fithis/her face. 3) Once the measured aerosol leakage drops below theaccepted threshold ensuring proper fit, the wireless sensorautomatically signals the camera to capture the image of the respiratorin its correct fit position on the worker's face. 4) The captured imageis analyzed and saved to be used as reference in the future whenever theworker dons a respirator, to ensure consistent respirator fit positionon the worker's face. The image may be captured at any point during thetest, such as before the test begins, to be subsequently linked to thefit value determined by the wireless aerosol sensor system.

The term “fit position” describes the configuration, position andorientation of the respirator on the user's face. Fit position includesposition of nose clip, shape of nose clip, position of straps,orientation on the face. An imaging sensor may include a traditional RGBsensor and may also include a NIR camera, depth sensor, and the like.

The worker may compare the “fit position” image with the currentplacement of the respirator on the worker's face. Adjustment to therespirator fit may be made until the “fit position” matches orsubstantially matches the current placement of the respirator on theworker's face.

Objects and advantages of this disclosure are further illustrated by thefollowing examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this disclosure.

EXAMPLES

All parts, percentages, ratios, etc. in the examples are by weight,unless noted otherwise. Solvents and other reagents used were obtainedfrom Sigma-Aldrich Corp., St. Louis, Mo. unless specified differently.

Sodium Chloride Aerosol Sensor

Sensor elements were constructed according to the method described inFIG. 5A and FIG. 5B and evaluated for respirator fit testingapplications.

The electrical impedance of a medium is a function of the number ofmobile charge carriers in the medium, the unit charge of the carriers,as well as their opposition to motion induced by coulombic forces. As aresult, the electrical impedance of a liquid solvent with a dissolvedionic solute is generally a function of the concentration of the solute.A sensing element, such as the one described above, may be used to probethe electrical impedance of a medium by contacting the electrodes withthe medium and monitoring the resistance to an applied electric field.In fluid media, such as water, the electric field is typically analternating field at a prescribed frequency which can provide bothresistive and reactive impedance information.

As an example, FIG. 11 shows the electrical impedance, specifically theimpedance magnitude, phase shift, resistance and reactance as a functionof frequency, of a sensing element such as the one described above whenimmersed in water/sodium chloride solutions of different concentrations.FIG. 11 top row are graphs illustrating the sensor response to differentconcentrations of NaCl in water, the resistance (solid lines) andreactance (dashed lines), as a function of frequency, measured by thesensor when coated with a liquid layer of the solution indicated.R=resistance, X=reactance. FIG. 11 bottom row are graphs illustratingthe sensor response to different concentrations of NaCl in water,corresponding impedance magnitude (solid lines) and phase shift (dashedlines), as a function of frequency, measured by the sensor when coatedwith a liquid layer of the solution indicated. Z=impedance magnitude,Theta=phase shift.

The impedance data is recorded by a Precision Impedance Analyzer 4294Aavailable from Agilent, USA. A significant decrease in the impedancemagnitude and resistance of the media (plotted on a log scale) is seenwith an increase in conductivity, as well as shifts in the overallprofile of all the curves. While this example is a case of a liquidmedia and not an aerosol, the underlying mechanism of the measurementforms the basis of how the sensors described in this application may beused to measure solution ionizable aerosols, as described below.

The compositions described thus far may be configured to alter theperformance of a fluid ionizable aerosol sensing element. Exemplary datathat illustrates the principal is shown in FIG. 12A-12C. FIG. 12A-12Care graphs that illustrate a comparison of isothermal water uptake andNaCl aerosol response for different surface modification and coatingsystems applied to a salt aerosol sensor.

The setup for the experiment used to generate the data in FIG. 12A-12Cis as follows: a fluid ionizable sensing element, with a pair ofinterdigitated conducting electrodes on the surface, is connected to anelectrical impedance spectrum analyzer. At t=0, the impedance spectrumrecording of the sensor begins. At t=60 s, the sensor is placed into atest chamber which is flowing air at 15 liters per minute, withapproximately 95% relative humidity. The sensing element is in fluidcontact with a portion of the flow. At the indicated time in each plot(‘NaCl aerosol on’), an aerosol containing approximately 10 μg/L NaClaerosol, with a mass mean particle diameter of 2 micrometers, isintroduced in the flow stream. The aerosol stream is generated byatomizing a NaCl/water solution of approximately 5 wt % NaCl using anatomizer. The aerosol stream is then removed at the indicated time(′NaCl aerosol off).

For the duration of the experiment, the sensing element is approximatelyin thermal equilibrium with the air stream, and the temperature of theairstream is constant. FIG. 12A shows the response of an exemplarysensing element with no surface modification to change the surfaceenergy, FIG. 12B shows that of a sensing element with theplasma+zwitterionic silane surface modification (described in FIG. 5A),and FIG. 12C that of a sensing element with the plasma+zwitterionicsilane surface modification with an additional glucose layer (asdescribed in FIG. 5B).

FIG. 12A illustrates the sensing element with no surface modification orcoating layer shows no significant change in electrical impedance at anypoint during the experiment.

This sensing element with no modification does not have a strongaffinity to form a fluid layer on the surface, and therefore lacks astrong mechanism in which the NaCl aerosol particles may ionize on thesensing element.

FIG. 12B illustrates that the sensing element with onlyplasma+zwitterionic silane treatment results in a small decrease inimpedance in response to humid air, and an additional decreasethroughout the duration of NaCl aerosol exposure. A small increase inimpedance once the aerosol stream is removed is likely due to a smallchange in humidity introduced by the NaCl aerosol stream.

This sensing element with only the plasma+zwitterionic silane treatmentenables a hydrophilic surface on the electrodes, which promotes someamount of fluid condensation, however at thermal equilibrium, thedriving force for fluid formation on the surface is lower than that ofthe sensing element with the additional hygroscopic material layer (FIG.12C).

FIG. 12C illustrates the sensing element with plasma+zwitterionic silanesurface treatment and also the glucose layer shows a much moresignificant response to the humid air stream, and then to the NaClaerosol stream. This is due to the hygroscopic property changes of thesensing element introduced by the addition of the glucose (hygroscopicmaterial) layer.

An example of how changing the coating weight of the hygroscopicmaterial layer may impact the sensing element response is shown in FIG.13A-13D, which illustrates the results of an experiment similar to thatof FIG. 12C, with variations in hygroscopic layer coating weight. FIG.13A-13D are graphs that illustrate a comparison of isothermal wateruptake and NaCl aerosol response for zwitterionic siloxane surfacefollowed by different coat weights of glucose applied to the saltaerosol sensor.

FIG. 14A-14C are graphs that illustrate a comparison of isothermal wateruptake and NaCl aerosol response for sensors with and without a filterelement. An example of how a particulate filter may be used to create areference electrode pair, as described in FIG. 7 and FIG. 8, is shown bythe data in FIG. 14A-14C.

All tests are conducted with the sensing element in the flow stream of ahumidity controlled NaCl aerosol system. The aerosol is generated byatomizing a solution of 5 wt % NaCl in water using an atomizer. Thehumidity of all tests is between 95% RH and 100% RH. The sensing elementin all tests is an interdigitated array, with 5 mil line/space widths ofthe digits, with ˜0.5 cm² area. The graphs show the impedance magnitude(solid lines) and phase shift (dashed lines) over time at five differentfrequencies. The impedance data is recorded by a Precision ImpedanceAnalyzer 4294A available from Agilent, USA.

For example, FIG. 14A shows the response of a sensing element,substantially similar to those described in this application, with noparticulate filter, which is inserted into an airstream containingaerosolized sodium chloride microparticles and nanoparticles.

FIG. 14B shows a similar experiment, where the aerosolized solution doesnot contain sodium chloride, such that aerosolized solution producesonly water vapor without sodium chloride particles.

FIG. 14C shows the result of the same experiment as that in FIG. 14A,except that the sensing element is configured with a particulate filteras described previously. The similarities of the response shown in FIG.14B and FIG. 14C demonstrate that the particulate filter adequatelyallows the fluid components, such as water vapor, to contact thereference electrode pair, but prevents the particulate matter fromcontacting the reference electrode pair.

Thus, embodiments of FIT-TEST METHOD FOR RESPIRATOR WITH SENSING SYSTEMare disclosed.

All references and publications cited herein are expressly incorporatedherein by reference in their entirety into this disclosure, except tothe extent they may directly contradict this disclosure. Althoughspecific embodiments have been illustrated and described herein, it willbe appreciated by those of ordinary skill in the art that a variety ofalternate and/or equivalent implementations can be substituted for thespecific embodiments shown and described without departing from thescope of the present disclosure. This application is intended to coverany adaptations or variations of the specific embodiments discussedherein. Therefore, it is intended that this disclosure be limited onlyby the claims and the equivalents thereof. The disclosed embodiments arepresented for purposes of illustration and not limitation.

1. A sensor comprising: a housing, wherein the housing has an openingconfigured to receive a sensing element; an electric circuit operablyconnected to the housing, wherein the electric circuit is configured todetect at least one electrical characteristic across at least one pairof electrodes positioned on the sensing element; at least one gas-movingelement in electrical communication with the electric circuit; and areader in communication with the electric circuit, wherein the reader isconfigured to compare information about a gas volume external to thehousing with information about a gas volume within the housing.
 2. Thesensor of claim 1, wherein the shape of the opening matches thecross-sectional shape of the sensing element.
 3. The sensor of claim 2,wherein a detection surface of the sensing element comprises the atleast one pair of electrodes.
 4. The sensor of claim 3, wherein thehousing further comprises at least one gas intake opening and at leastone gas exhaust opening configured to direct a predetermined flow rateof gas to contact the detection surface of the sensing element afterwhich the predetermined flow rate of gas is forced out of the housing bythe gas-moving element.
 5. The sensor of claim 4, wherein the detectionsurface of the sensing element is oriented substantially perpendicularto the predetermined flow of gas.
 6. The sensor of claim 1, wherein theelectric circuit is affixed to the housing.
 7. The sensor of claim 1,wherein the electric circuit is positioned within the housing.
 8. Thesensor of claim 7, wherein the electric circuit is affixed to at leastone interior wall of the housing.
 9. The sensor of claim 1, wherein,when the sensing element is inserted in the opening, there issubstantially no fluid communication from the outside of the housing tothe inside of the housing through the interstitial space between theopening and the sensing element.
 10. The sensor of claim 1, wherein thegas comprises particulates.
 11. The sensor of claim 1, wherein theelectrical characteristic is at least one of resistance, inductance,capacitance, and electrical impedance.
 12. The sensor of claim 1,wherein the sensor comprises a heating element configured to increasethe temperature of at least a portion of a sensing element surface. 13.The sensor of claim 1, wherein the sensor is configured to applyelectrical power to at least one heating element on the sensing element.14. The sensor of claim 1, wherein the sensor comprises a coolingelement configured to decrease the temperature of at least a portion ofa sensing element surface
 15. A respirator fit test system comprising asensor according to claim 1.